A variety of procedures are utilized to obtain fibers from wood pulps, which fibers are used to make a number of different paper, paperboard, and other wood products. Depending upon the use to be made of the wood products, a variety of additives are added thereto for purposes of improving the opacity, brightness, strength, bulk, and other like properties in the products. With increased costs of additive materials for such purposes as well as increased costs in terms of recovery of the fibers, efforts have been made to increase desired properties in the final products while decreasing costs.
More specifically, with reference to paper making, for example, a variety of materials, such as aluminum and titanium oxides are added to increase the opacity and brightness of papers made from wood pulp fibers. These are costly additives, but presently necessary to obtain paper with adequate opacity and brightness. In addition, a variety of other additives and treatments have been attempted to increase the strength and bulk of the wood pulp fibers in order to obtain more square feet of paper per ton of fiber. This is an important consideration since it permits lighter weight paper which has significance to those who publish newspapers, magazines, and other materials that are sent through the mails.
Efforts to overcome the problems of costly additives and treatments have included a variety of processing techniques including freezing and freeze-drying, but these, heretofore, have themselves required equipment that was costly to purchase and/or operate or the need for chemicals to be present during such treatment which are detrimental in subsequent operations.